This invention concerns an airtight slide fastener. These type of fasteners are widely used in daily life because of the simple closing and opening mechanism by moving the slider, but they are defective in that they lack the airtightness as only plural pieces provided on the tapes engage with each other to effect closure and the tapes on which the engaging pieces are provided do not contact each other.
If a slide type fastener which would maintain complete airtightness were to be developed and used in containers or clothing comprising any kind of treated cloth or rubber sheet for keeping airtightness, then this would prove vastly meritorious in the industry. Many attempts have been made heretofore in this regard. A simple example of such prior attempts is a sliderless fastener, utilizing the flexibility of plastic materials. This prior device has a female groove on one edge of the plastic tape and a male ridge on the other edge for mutual engagement. However, while this fastener may remain airtight so long as the male part stays within the female part, the two are quite easily separated when a slight force is applied thereto. Thus, their use is limited to a very narrow field, such as for bags receiving merchandise.
Opening and closing of slide fasteners is conventionally effected by causing engagement of a plurality of engagement pieces or separation thereof. Therefore, it will be possible to maintain airtightness if the tapes on which the engaging pieces are provided can also be engaged in a tight-seal fashion at the time said engaging pieces are engaged with each other. However, the problem still remains that, if the fastener tapes of such a structure were to be closed and complete airtightness were to be obtained as the two tapes are engaged with each other, there would still be a slider at one end of the tape and the area around the slider would not be airtight, since the engagement of the tapes at this particular area would not be perfect.
In order that a complete airtightness of the slide fastener be obtained, it is necessary to provide the end of the tape with a special structure which would cause that part of the tapes that come within the slider to strongly adhere to the leader of the slider after moving the slider to close the fastener tapes.